09V/09VI (095/096) Nuclear Submarine Thread

[Tirdent]

A 1600t SSK may not have the endurance, weaponry, speed, and stealth that the PLAN requires of its SSKs, as even up to now you have not made a compelling case for the PLAN to switch to such a small SSK.

As mentioned before, the requirements change significantly once you limit the scope of the SSK's role to littoral ops. With modern AIP technology, small submarines can provide endurance which is perfectly adequate for that task - why pay for overkill which is of no benefit to the intended job? A submarine operating purely in a coastal environment does not need extreme speed and range. Silencing? I think you'll find the current generation of European SSKs does just fine in that regard (the Swedish sub the USN leased to hone their skills against was one of the smallest available).

So the case for smaller boats is patently obvious: cost. Your stated worry with relying on SSNs for blue water work is how expensive they are - well here's an opportunity to release non-trivial amounts of funding for just this purpose by moving to compact, exclusively littoral SSKs. It's a case of horses for courses: since a world-class nuclear-powered sub is so much better at open-ocean and expeditionary warfare, supplementing it in that role with large SSKs is false economy. Fewer SSNs in favour of greater displacement in each SSK is very probably an unfavourable trade-off in net capability.

Another point is that if the PLAN decides to add small nuclear plants to their SSKs to create hybrid designs, I seriously doubt a sub much smaller than the Yuan class is going to be in the works.

SSNs have been built as small as 2700t, and that was with established propulsion technology representing the state of the art from 30 years ago (Rubis). I'm sure it would be possible to do better today, especially with non-traditional solutions (RTG-powered Stirling?) .

 

[Anlsvrthng]

(RTG-powered Stirling?) .

No way, I calculated once, it require full output of Cs137 from dozens of commercial reactors to keep running a 3000 t. class submarine.

And other forms are out of question, you can not make enough Pu239 even for a car, not for a submarine.
And the Pu239 way more expensive than the highest grade of Pu238.

 

[Iron Man]

As mentioned before, the requirements change significantly once you limit the scope of the SSK's role to littoral ops. With modern AIP technology, small submarines can provide endurance which is perfectly adequate for that task - why pay for overkill which is of no benefit to the intended job? A submarine operating purely in a coastal environment does not need extreme speed and range. Silencing? I think you'll find the current generation of European SSKs does just fine in that regard (the Swedish sub the USN leased to hone their skills against was one of the smallest available).

So the case for smaller boats is patently obvious: cost. Your stated worry with relying on SSNs for blue water work is how expensive they are - well here's an opportunity to release non-trivial amounts of funding for just this purpose by moving to compact, exclusively littoral SSKs. It's a case of horses for courses: since a world-class nuclear-powered sub is so much better at open-ocean and expeditionary warfare, supplementing it in that role with large SSKs is false economy. Fewer SSNs in favour of greater displacement in each SSK is very probably an unfavourable trade-off in net capability.

It's not just a matter of blue water vs littorals. Endurance is also about how long can you skulk around underwater in one location without having to rise up to snorkel, and how long your crew can survive on the supplies they can pack into a given hull. A smaller SSK will certainly be significantly more limited in this aspect compared to a large SSK, regardless of whether the deployment is to a littoral or to a blue water zone.

SSNs have been built as small as 2700t, and that was with established propulsion technology representing the state of the art from 30 years ago (Rubis). I'm sure it would be possible to do better today, especially with non-traditional solutions (RTG-powered Stirling?).

Yes, but that was a nuke plant only submarine. We are talking about a hybrid which combines a nuke plant with a conventional plant in one hull, so the example of the Rubis is not relevant to the discussion.

 

[Tirdent]

It's not just a matter of blue water vs littorals. Endurance is also about how long can you skulk around underwater in one location without having to rise up to snorkel, and how long your crew can survive on the supplies they can pack into a given hull. A smaller SSK will certainly be significantly more limited in this aspect compared to a large SSK, regardless of whether the deployment is to a littoral or to a blue water zone.

At one point the record holder for underwater transit in actual operation without snorkeling was the 1800t Type 212 (18 days - that's pretty decent when you have only a short transit to/from the area of operations because you stay in your own back yard). Wasn't there talk of the 3600t Yuan class having put up a new endurance record recently? How did that performance compare to the Type 212?

Bear in mind that, as alluded to above, at least part (possibly all) of any advantage for the Yuan will be driven by accommodating longer transit distances in blue water ops that would be irrelevant for a littoral sub. Even if Yuan does perform somewhat better it may very well be that both are designed for the same in-theatre patrol duration (with Yuan simply having to allow for that theatre potentially being a lot farther away).

Yes, but that was a nuke plant only submarine. We are talking about a hybrid which combines a nuke plant with a conventional plant in one hull, so the example of the Rubis is not relevant to the discussion.

In a hybrid architecture (nuclear power output sufficient for patrol speed only, dash provided by battery/snorkeling) you'd be able to radically downsize even a conventional nuclear plant. We are talking about a difference of at least an order of magnitude in power output!

That should go a long way toward accommodating a bigger diesel (there already is one for emergency propulsion) along with correspondingly larger fuel bunkerage and battery bank. Especially since you would not need to scale the latter up by the same factor, because you'd probably reduce the top speed requirement to an SSK-like level.

If you can get rid of the steam turbine in a non-traditional nuclear plant, so much the better.

No way, I calculated once, it require full output of Cs137 from dozens of commercial reactors to keep running a 3000 t. class submarine.

How much power do you reckon it takes? A couple of hundred kilowatts of AIP power should suffice - you don't need to provide enough to drive the electric motor at full load, it's supposed to be used for extended patrol, not dash. I'm definitely no expert on nuclear materials, so I can't speak to that part of the issue.

 

[Tam]

Feel free to go right down to 1600t, if that seems more compelling to you. It's not necessarily all about superiority either, but simply strict sufficiency - why pay more than you absolutely have to in order to get the job done? Use the savings for more SSNs, that probably gets you more blue water capability in the final reckoning than continuing to rely on 4000t SSKs.

Even if you have the money, you cannot produce more SSNs than what the designated shipyard can produce. Probably two per year just guessing from the new Bohai shipyard. Wuhan on the other hand, seems to have the facilities to produce as many as four Yuans. Why limit to producing only SSNs when you can produce both SSNs and SSKs, without reducing the number of SSNs needed. You do have to realize that the Bohai shipyard also has to produce SSBNs.

As mentioned before, the requirements change significantly once you limit the scope of the SSK's role to littoral ops. With modern AIP technology, small submarines can provide endurance which is perfectly adequate for that task - why pay for overkill which is of no benefit to the intended job? A submarine operating purely in a coastal environment does not need extreme speed and range. Silencing? I think you'll find the current generation of European SSKs does just fine in that regard (the Swedish sub the USN leased to hone their skills against was one of the smallest available).

I don't see how suddenly changing to a new small class would be cheaper than a larger one that is already on production. You may end up making smaller but more expensive subs versus bigger but cheaper submarines because the later has been volume produced. With every new Yuan, the price for each unit goes down.

As for endurance, I don't know if other subs tried their own endurance records, and even if they did, they may choose to keep it classified. Both the Yuan's endurance and depth record is classified, with the latest attempts claiming to beat their own existing record. For depth I only see 400 meters based on internet sources, which is deeper than the 250 meters of the Type 212. This is like the guy who ran the track and gets the record because he choose to make it public, even if others may have ran the track faster but kept it secret.

Sensors are also a matter of size. Low frequency sonars have to be bigger and longer because of physics, and that's what you need for longer ranged detection.

As for quietness, you need to compare with the relative sophistication of the submarine per country. Given that the Chinese may not be as sophisticated as the Europeans with their SSK tech (yet), the bigger size would be needed to compensate for the gap in acoustic reduction technology. You also have to ask yourself if the same tech used on the Gotland is applied on a 3500 ton SSK, would it be even quieter than the 1500 ton sub? For that matter, if the Germans built a 3500 ton SSK based on the Type 212 tech, would this sub have even more endurance than the Type 212?

The next question is how much would this bigger subs cost more than the 1600 to 1800 ton subs?

 

[Anlsvrthng]

How much power do you reckon it takes? A couple of hundred kilowatts of AIP power should suffice - you don't need to provide enough to drive the electric motor at full load, it's supposed to be used for extended patrol, not dash. I'm definitely no expert on nuclear materials, so I can't speak to that part of the issue.

1kg of Cs137 generate approx 250-450 watts of heat,depending the capability to capture the gamma photons in the heating zone.
On GW of commercial electricity generating capacity makes 30kg of Cs137/year.
That is the most significant, medium term decay product.
Half life is 30 years.

Other candidate is Sr90, 530 w/kg, 22.5 kg/year for each GWe capacity.

All above data is approximation .
So, to make 200 kWe electrical capacity , with 20% of efficiency you need 2000 kg of Sr90, that in turn require 100 reactor years to make for 1 GWe commercial reactor.
After 30 years the electrical output will drop to half.

So it needs from 6 reactors of 30 years of waste to make the heat source, and afterwards it needs two reactor full output to keep it on level.

China has 40GWe reactor capacity, so by reprocessing all waste from them it is possible to start maybe 7 submarine, with 1 MW thermal capacity each.
It is possible to increase the number maybe to 12 with Sr90+Cs137.

 

[antiterror13]

I think it is safe to say in ten years time the US will start to make SSKs, to counter the Russian/Chinese subs operating around the US littoral waters.

I am hoping way less than 10 years when Chinese/Russian subs operation around the US littoral water ... and also the warship around the US water ....to protect Freedom of navigation (FON)

 

[Deino]

Guys .... are we still in the 095/096 Nuclear Submarine Thread or has this become a regular submarine warfare thread?

Especially FON of Chinese Russian subs in US waters is more than off-topic

Please stay on topic

 

[Anlsvrthng]

I started to imagine the challenges of MW range RTG powered submarine supply chain, and I think it is way more expensive and difficult than anyone can imagine first.
The main problem is no the isotope in the reactor, but reprocessing / storing /handling/installation of the isotopes safely - main challenge is the cooling.

Only the Sr90 can be candidate due to this challenges, but still the periodic removing , cooling during handling has to provided, and this doesn't looks as a cheap stuff.

After all of that I think it is safe to say that considering the full infrastructure cost the reactors are still cheaper.

 

[gelgoog]

Forget RTG generation. It generates too little power for a submarine. Also, the heat generated is low grade heat so the conversion efficiency into motive power is really low (think Carnot cycle). Even if you use alternative methods to convert the heat into power, say thermoelectric generators, the conversion efficiency of the heat into electricity is like 15%. RTGs are mainly useful for things like sonar buoys in the middle of nowhere. Think of it like a long duration backup battery for some device you will not have easy access to. Also Strontium-90 is really problematic because it is a beta emitter and it is highly carcinogenic. There is a reason why people typically stick with the much milder alpha emitter isotopes.

I think the LWRs are still the best choice. It might be possible to use some other way to convert the heat into motive power. But other than that there are not a lot of choices with regards to reactor design given current technology. There are other reactor designs, for sure, but they have their own issues. The Soviets used lead-cooled fast reactors in the Alfa-class submarine for example. But it has a lot of issues, like, when you power it down the coolant solidifies and then you need to melt it down with heat before you start the reactor again. It is a real issue and made them go back to LWRs in later series. Sodium-cooled fast reactors are a no-no in a submarine. The sodium coolant burns in contact with water. Then there are things like pebble-bed and prismatic nuclear reactors. Of those I think the prismatic nuclear reactors make the most sense. But their main advantage is to have lower weight and be more compact. Which is not that big of a deal for something like a submarine. I think the advantage of sharing much of the technology with civilian nuclear reactors make LWRs the most practical choice.